For the first time, extreme heat has been formally recognised alongside long-standing public health challenges such as non-communicable diseases (NCDs).
The announcement was made as more than 300 representatives from over 70 cities convened last week in Rio de Janeiro for the 2026 Partnership for Healthy Cities Summit.
For nearly a decade, urban health leaders convening under the Partnership for Healthy Cities have focused on major risk factors, including tobacco use, road safety, air pollution, and unhealthy diets. Together, according to the World Health Organisation (WHO), these risks contribute to NCDs and injuries that account for more than 80 percent of global deaths.
This year, however, the agenda expanded to include heat, an increasingly severe threat that experts say has long been overlooked despite its rapid intensification.
“Heat is currently responsible for an estimated half a million deaths globally each year, and that number is rising. Against this backdrop, cities are on the front lines,” said Dan Kass, an expert in environmental health and disease prevention and a Senior Vice President of Environmental, Climate and Urban Health at Vital Strategies.
Despite its growing toll, heat has long remained underrepresented in global health discussions. Unlike infectious diseases or acute disasters, its effects are often indirect, cumulative, and poorly classified. “National health systems record heat-related deaths only when conditions like heatstroke are explicitly diagnosed,” added Kass.
However, experts emphasise that this captures only a fraction of the true burden. “Heat exacerbates underlying illnesses, including cardiovascular disease, respiratory conditions, and kidney disorders, transforming manageable conditions into fatal ones,” Kass said.
According to Kass, for every death officially recorded, many more likely go uncounted due to attribution gaps. This underreporting has delayed policy attention, but the data is becoming increasingly difficult to ignore.
The State of the Global Climate 2025, released by the World Meteorological Organisation (WMO) on March 30, highlights extreme heat as one of the deadliest climate-related hazards. The report documents rising heatwave frequency and intensity, linking them to increased mortality, overstretched health systems, disrupted livelihoods, and growing mental health pressures.
And according to experts, urban cities continue to bear the brunt. “Urban areas are disproportionately affected due to the “urban heat island’ effect. Dense materials such as concrete, asphalt, and steel absorb and retain heat, driving temperatures significantly higher than in surrounding rural areas,” explained Kass.
A 2022 UN-Habitat research shows that daytime urban temperatures can be up to 3°C higher, while nighttime differences can reach as much as 10–12°C. This nighttime heat retention, experts say, is particularly dangerous because it removes the body’s opportunity to recover from daytime exposure, creating continuous physiological stress.
“Even small temperature increases can significantly elevate mortality risk, especially among vulnerable populations,” explained Kass.
Inequality further amplifies this risk, as low-income communities often lack access to cooling, green spaces, and adequate housing, making them disproportionately exposed. According to the UN-Habitat, over 1 billion people globally live in informal settlements, many of which are highly heat-exposed due to poor infrastructure and limited services.
And nowhere are these vulnerabilities more acute than in rapidly urbanising regions of Africa. The World Bank estimates that Africa’s urban population will double by 2050, adding pressure to already strained infrastructure and increasing exposure to climate hazards.
In Accra, heat-related illness is already becoming visible in routine health data. According to city health officials, heat stroke cases are now among the leading outpatient conditions, alongside respiratory illnesses exacerbated by air pollution.
“Heat is something we are seeing in our health data every day,” said Florence Sumala-an Kuukyi, a public health engineer at Accra Metropolitan Assembly in Ghana.
And climate change is a key driver of this trend. The Intergovernmental Panel on Climate Change (IPCC) reports that Africa has warmed at a rate slightly above the global average, with temperatures increasing by approximately 0.3°C per decade since 1991. This warming is intensifying heat extremes while compounding existing vulnerabilities.
In Nairobi, historically known for its temperate highland climate, heat exposure is rising in less obvious but increasingly dangerous ways. While temperatures rarely exceed formal heatwave thresholds (around 32°C), the frequency and persistence of warm days are increasing.
According to a Climate Central report, in 2024, more than 14 million Kenyans experienced at least 60 days of high-risk heat, defined as temperatures exceeding 90 percent of the historical baseline.
On the other hand, the Kenya Meteorological Department reports a steady rise in average temperatures across the country, with an increase of about 1.0–1.5°C since the mid-20th century. Additionally, urban expansion is intensifying localised heating, with satellite analyses like the Landsat-based studies, 2010–2023, showing that land surface temperatures in densely built areas of Nairobi can be 4–7°C higher than nearby vegetated zones.
Against this backdrop, informal settlements face the greatest risks. “Limited ventilation, high building density, and restricted access to water and shade significantly increase heat exposure, particularly for children, older adults, and people with pre-existing conditions,” explains Dr Joyce Kimutai, an Attribution Scientist at the Kenya Meteorological Department.
In the meantime, the growing recognition of heat as a public health crisis is driving a shift in how cities respond. “Governments are now redefining heat not just by meteorological thresholds, but by its health impacts, linking temperature data with hospital records to estimate excess mortality,” added Kass.
Cities like Accra are already implementing comprehensive strategies, including heat mapping, identification of high-risk zones such as markets and transport hubs, and interventions like cooling centers and urban greening.
“Tree-planting initiatives and reflective infrastructure are also being scaled up to reduce ambient temperatures,” adds Kuukyi.
According to Kass, this reflects a broader transition from awareness to action. “Cities are adopting multi-layered approaches, including improving data systems, developing heat action plans, targeting vulnerable populations, and investing in physical cooling solutions such as expanded green spaces and reflective materials.”
On the other hand, some cities are also deploying low-cost temperature sensors to produce hyper-local heat maps, revealing sharp temperature differences within neighborhoods and enabling more targeted interventions.
At the same time, Kass said, communication strategies are evolving to emphasize that apart from being an environmental issue, heat is a serious health risk.
